issue with Berger 105 hybrids and N150

[Deleted old_dood]

I determined a load with this combo of 29.6 grains using brass that had 20+ uses. Bullets were jumped about .008. today I loaded 50 in cases that had only been fired once, same amount of powder and jump. On the first two shots I got severely heavy bolt lift and ejector impressions on the base. I stopped shooting, got home and verified 29.6 grains powder. That load is well below what my Berger manual specifies as maximum. Both the old cases and the newer ones were sized with the same die. the necks were dry lubed prior to installing bullets.

can anyone speculate why this happened?

 

[CaptainMal]

Not with Norma 150 but with Varget, I had severe carbon fouling built up. It took lots of C4 Carbon cleaner and Isso bore paste to get the barrel back to working at a reasonable pressure.

 

[spclark]

Purely speculative (that's what you asked for, right?) is that the 20+fired cases were work-hardened enough from the previous firings to better withstand the pressure. The newer cases, all else being equal, exhibited a greater tendency to expand under pressure and spring back somewhat less prior to extraction.

If you have a blade micrometer handy, try measuring the diameters of a sampling of both case lots at the extractor groove bottom, just ahead of the extractor groove, and about 0.060" ahead of the groove.

These are 6BR cases right? From fairly close batches, year-wise?

If the old cases are 'years' older there may be case volume / brass alloy differences too. Lapua's cardboard box stuff was different from the newer blue box product....

 

[Deleted old_dood]

Purely speculative (that's what you asked for, right?) is that the 20+fired cases were work-hardened enough from the previous firings to better withstand the pressure. The newer cases, all else being equal, exhibited a greater tendency to expand under pressure and spring back somewhat less prior to extraction.

If you have a blade micrometer handy, try measuring the diameters of a sampling of both case lots at the extractor groove bottom, just ahead of the extractor groove, and about 0.060" ahead of the groove.

These are 6BR cases right? From fairly close batches, year-wise?

If the old cases are 'years' older there may be case volume / brass alloy differences too. Lapua's cardboard box stuff was different from the newer blue box product....

that sounds like it may be likely. I tried chambering the fired cases afterwards and couldn't. the brass is over a year apart. I don't have that tool. wouldn't the ejector impression indicate too hot a load? the ejector impression would be an indication of excessive pressure against the bolt face. I'm trying to understand how work hardened case sides would prevent the ejector impression on the older brass. anyway, I'm starting from scratch to work up a load with the new brass.

 

[Jason Boersma]

The new cases might have less internal case capacity, plus you might have a carbon ring that would cause a sudden increase in pressure

 

[spclark]

You seeing an impression from the ejector or a slight scraping from the bolt being turned while the case is pressed against it?

I doubt brass lots differ much if only a year apart, both blue box but I guess it's possible.

Do your multi-times fired cases chamber freely after firing?

 

[Deleted old_dood]

it's a definite round impression on both cases. where you said to measure the cases, there was a difference of one to two thousandths. after getting down to a clean barrel I applied Iosso to 3 patches and scrubbed just in front of the chamber 10-15 strokes each. I realize there's no way of knowing if that's enough. The barrel has about 300 rounds down it. still don't understand how this could happen being well under Bergers recommended maximum load with that bullet. Right afterwards I shot about 90 loads of the 80g varmint FB, jammed .006, 31g IMR4895, in the old cases with no issues.

 

[rain164845]

Have the cases grown in length? Try trimming.

 

[spclark]

Work-hardened brass behaves differently than newer brass, which is why we anneal case necks & sometimes shoulders.

What I'm thinking is that your older brass tends to spring back after firing while the newer stuff tends to stay hard against the chamber walls. At the same time your older case heads, being 'tougher', resist being deformed by the ejector better.

If that two thousandths growth is at the extractor groove base or the case web just in front, the loads are too high for fresh brass. A couple firings with slightly reduced loads will reduce this tendency of brass to flow. Sometimes small base dies can help to keep this under control if 'sticky bolt lift' evidences itself with repeated firings.

Vihta Vouri products are usually pretty uniform lot to lot. If by chance you've changed lots recently you may be seeing a concantenation of variables that produce pressures that reveal themselves in what you're seeing.

Knowing how thoroughly you've cleaned your barrel is what a borescope can tell you once you get familiar with what they reveal & how to interpret it. If you know someone who owns one, perhaps you can arrange to have them show you what's otherwise inaccessible to our unaided eyes.

 

[BradY]

Simple test, go back to the old load before the hybrids and try. Assuming you have only just started using the hybrids that is. If the cases work fine my bet is you have a batch of fat 105 hybrids and need to back the powder charge off way down and re work up. People told me that 32+gr of H4895 in a dasher produced just under 3000fps. Im at 3015 with 105 hybrids in a 236 barrel with only 31.7gr. Those projectiles do measure quite large on the pressure ring. Aside from that they are fantastically accurate.

 

[22BRGUY]

Probably silly question but is it possible you could have forgot to remove all sizing case lube or any type of lube in the chamber? I remember doing that at one time with similar results. Hope you find the issue.

 

[dkhunt14]

it's a definite round impression on both cases. where you said to measure the cases, there was a difference of one to two thousandths. after getting down to a clean barrel I applied Iosso to 3 patches and scrubbed just in front of the chamber 10-15 strokes each. I realize there's no way of knowing if that's enough. The barrel has about 300 rounds down it. still don't understand how this could happen being well under Bergers recommended maximum load with that bullet. Right afterwards I shot about 90 loads of the 80g varmint FB, jammed .006, 31g IMR4895, in the old cases with no issues.

Most times you can feel the carbon when cleaning. When you put a wet patch in your bore guide and start it down the bore if it pushes hard then gets easy; you have carbon buildup. Another reason the newer cases might be showing ejector mark is they are softer and bumping a lot harder. Now that they are bumped harder they have a smaller capacity and are being driven in the chamber farther when fired. They then bounce back against the bolt face and ejector. I have seen cases bump as much as 10 thousandths more after being annealed. Matt

 

[Deleted old_dood]

went back to the range today with a new ladder test and 18 of the newer brass. I started off at the Berger recommended start load of 27.5g N150. three shots each with a .3g increment. my maximum was 29.0. at 100 yards I had one hole groups at 28.4 and 29.0. There were no pressure signs. the six groups all showed the same verticle. I've read the thread "long range load development at 100 yds". Is is possible my node is that wide? 27.5-29.0 grains?

what I plan on now is to load the rest of the new brass with no more than 29.0 and then, on subsequent reloads, try a few at a higher load to see how they react.

One thing I forgot to mention in the OP was that the older brass had been neck turned just to even them out. these were sized with a .265 bushing. the new brass was not neck turned and was sized with a .266 bushing.

 

[Deleted old_dood]

Possible solution

DKHunt14 sent me a pm asking if I was sure my new barrel had a no-turn neck chamber. Since it was a Savage pre fit I assumed it did. I checked to see if I could push a bullet into the fired, new cases before resizing. I could not. With my old, neck turned cases, before resizing, I've always been able to slide a bullet into the neck. I guess I'll be calling Criterion with the diameter of a loaded round at the neck and see what they say.

 

[venatic]

Sounds like the dreaded donut to me? I have seen that problem in my 308 with cases sized with a bushing die numerous times.

 

[dkhunt14]

Sounds like the dreaded donut to me? I have seen that problem in my 308 with cases sized with a bushing die numerous times.

He said the cases were only fired once or twice and they shouldn't have a donut. matt

 

[fm1947]

savage prefit, did you use a go gage?

 

[Deleted old_dood]

yes, GO and NOGO. I'm beginning to think its just a question of treating new brass as one would treat a powder or bullet change. I mistakenly posted that bullets wouldn't fit into fired cases when, in fact, they do.

 

[Deleted old_dood]

more on this problem. I went back to the range with another ladder test using the new brass, same powder and bullets. this time I cleaned every 15 rounds with a patch of Lock-ease after every cleaning. I'd get random heavy bolt lift all throughout the test (but never right after the patch with Lock-ease). The load that I originally had a problem with, 29.6g, shot without incident. I was able to shoot all the way up to 30.2g. there were 10 different loads and all throughout, I'd get a random, very heavy bolt lift. I thought about a majority of responses here suggesting a carbon ring and I remembered something that was apparent to me after installing the new barrel.

I installed this new barrel around January but didn't start shooting until early April. On my old factory barrel, when I'd press a bullet into the lands, it would got to a certain point and then stop. On the new Criterion, the bullet will go to a certain point with minimal force and stop, but then, if I push a little more, it will go further. This is when using the Hornady OAL tool. the difference between first feeling resistance and the point where the bullet absolutely stops, is over .100. Since I'd never installed a 3rd party barrel before I wasn't sure if I should be concerned about these findings. Now I'm beginning to wonder if the chamber on my barrel was not cut correctly. BTW, the second point where the bullet stops, seems to be the correct one based on the typical OAL I'm getting compared to the OAL's I was getting with the original factory barrel. Again, this was noticed before I ever fired a round through the new barrel so it couldn't be a carbon ring.

Does anyone thing I have a cause for concern due to this?

 

[spclark]

A thread on seating into, touching, or off the lands (specifically in .223) on another forum brought to my attention that three of the most commonly seen chamber reamers for service rifle cut necks to 0.2240" dia., exactly the same as that of the bullets being used.

The specific post engendered my questioning how a bullet seated off the lands could get stuck when chambered if the round were subsequently extracted without being fired. The answering post gave a chart presenting eight reamer profile dimensions. The other five had scant (0.0002") clearance up to vast (0.0030") so I'm wondering if maybe your new barrels throat is similarly 'no clearance' at 0.2430" while random Bergers may be 0.243x?